1. Field of the Invention
The present invention relates to an electrochemical cell.
2. Description of the Related Art
As electrochemical cells such as a nonaqueous electrolyte secondary battery and an electrical double layer capacitor, there are electrochemical cells formed in button shapes (in the following explanation, including a coin shape and a cylinder shape). The button-type electrochemical cells are used in, for example, power supplies of various devices. As one form of the button-type electrochemical cells, for example, a battery disclosed in JP-A-2002-298803 (Patent Literature 1) described below is proposed.
Patent Literature 1 discloses a configuration in which a negative electrode case made of metal functioning as a negative electrode terminal as well and a positive electrode case made of metal functioning as a positive electrode terminal as well are fit with each other via an insulating gasket. Specifically, in Patent Literature 1, the positive electrode case is fit with the negative electrode case via the insulating gasket by caulking. In an inner space defined by the positive electrode case and the negative electrode case, an electrode body is included together with a nonaqueous electrolyte.
However, when the negative electrode case and the positive electrode case are caulked, in some case, the negative electrode case and the positive electrode case are damaged by a caulking load acting on the cases during the caulking and airtightness on the inside of the battery is deteriorated. When the caulking is performed in a state in which foreign matters are held between the cases, in some case, a gap is formed between the negative electrode case and the positive electrode case by the foreign matters and the airtightness on the inside of the battery is deteriorated.
Further, when the cases are sealed from each other by the caulking, in order to mechanically increase the airtightness, it is necessary to impart strength enough for withstanding the caulking load to the negative electrode case and the positive electrode case. Therefore, the thickness of the negative electrode case and the positive electrode case increases, effective volume for housing the electrode body decreases, and energy density decreases. Therefore, in the electrochemical cells in the past, there is room of improvement in terms of improving the airtightness to improve reliability and improving the energy density.